Add BCC to certain store emails

wc-bcc-emails.php

/**
 * Add BCC to certain store emails.
 *
 * @param  string $headers
 * @param string $email_id
 * @return string
 */
function kia_add_bcc_to_specific_emails( $headers, $email_id ) {

    $bbc_these_emails = array(
        'customer_completed_order', // Add other emails as entries in this array.
    );

    if ( in_array( $email_id, $bbc_these_emails ) ) {
        $headers = array( 
            $headers,
            'Bcc: Me <my@mail.net>' ."\r\n", // Modify the email as needed.
        );
    }

    return $headers;
}
add_filter( 'woocommerce_email_headers', 'kia_add_bcc_to_specific_emails', 10, 2 );